1. Field of the Invention
The present general inventive concept relates to an electrophotographic image forming device, such as a laser printer, a digital photocopier, and a facsimile machine. More particularly, the present general inventive concept relates to a roller spacing apparatus to space apart two rollers (e.g., to space apart a photoconductive medium and a developing roller, or to space apart a photoconductive medium and a charging roller) that rotate in close contact with each other under a predetermined pressure and by a predetermined distance, and to maintain the two rollers in a non-contact state, such as when the two rollers are not in use (e.g., during shipping), and an image forming device having the apparatus.
2. Description of the Related Art
Generally, an electrophotographic image forming device, such as a laser printer, a digital photocopier, and a facsimile machine, comprises a photoconductive medium to form a developer image.
A charging roller, a laser scanning unit (LSU), and a developing roller are disposed at predetermined locations around an outer circumference of the photoconductive medium in a rotation direction. The charging roller charges a surface of the photoconductive medium with a predetermined electric potential, the LSU scans the surface of the charged photoconductive medium with laser beams and thereby forms an electrostatic latent image on the surface of the photoconductive medium, and the developing roller supplies a developer to the surface of the photoconductive medium and thereby forms a developer image corresponding to the electrostatic latent image.
The developing roller and the charging roller are rotated in close contact with the photoconductive medium under a predetermined pressure. The photoconductive medium, the developing roller, the charging roller, or each of them comprises an elastic layer, such as a rubber layer, to provide protection from a contact damage.
The image forming device maintains the photoconductive medium and the charging roller and/or the developing roller with the elastic layer in close contact until the image forming device is delivered to a user. As a result, the elastic layer is physically and permanently compression set to prevent high viscosity low molecular organic matter of the elastic layer to chemically-change and thus to come out from a surface of the elastic layer. The high viscosity low molecular organic matter is combined with the developer and adheres to the surface of the photoconductive medium. In this case, physical and chemical changes may cause device components to malfunction and may cause image degradation, deteriorating a reliability of the device. In some cases, a deformed roller, or even the image forming device itself, has to be replaced.
The photoconductive medium, the charging roller, and the developing roller are fabricated in the form of a process cartridge that integrates components into a housing as a single module unit, so that the components are easily detachable from a body of the electrophotographic image forming device for easy repair or replacement.
If the process cartridge fabricated for replacement is not in use, e.g., until it is mounted in the body of the image forming device after coming into market and being purchased by a user), the photoconductive medium and the charging roller and/or the developing roller are in close contact with each other during the period of non-use. Accordingly, there is a problem that the elastic layer of the photoconductive medium, the developing roller, and/or the charging roller may be physically or chemically damaged.
In order to address this problem, the image forming device or the process cartridge comprises an apparatus for spacing apart the charging roller or the developing roller from the photoconductive medium when not in use.
FIGS. 1 to 3 are views illustrating a roller spacing apparatus 1, which spaces apart a developing roller from a photoconductive medium when an image forming device is not in use.
The roller spacing apparatus 1 comprises a spacing member 30 disposed at a shaft 21 of a developing roller 1, and the spacing member 30 is movable between a first position and a second position. If the spacing member 30 is at the first position, the developing roller 20 is not spaced apart from a photoconductive medium 10, as illustrated in FIG. 2. If the spacing member 30 is at the second position, the developing roller 20 is spaced apart from the photoconductive medium 10 by a predetermined gap g, as illustrated in FIG. 3.
The spacing member 30 comprises a spacing protrusion 35 that is brought into contact with a stepped portion 12 of a driving gear 11 of the photoconductive medium when the spacing member 30 is at the second position, and spaces apart the developing roller 20 from the photoconductive medium 10 by the predetermined gap ‘g’.
The spacing member 30 is movable between the first and the second positions along a shaft 21 of the developing roller 20 by a spacing member moving part 40.
The spacing member moving part 40 comprises a first rotary member 41 and a second rotary member 42. The first rotary member 41 is idle-rotatable around the shaft 21 and the second rotary member 42 is rotatable integrally with the shaft 21 at a D-cut portion 22 of the shaft 21. The first and the second rotary members 41 and 42 are restricted by fixing members 48 and 47, respectively, so that the first and the second rotary members 41 and 42 do not move in a lengthwise direction of the shaft 21.
As illustrated in FIG. 3, the roller spacing apparatus 1 has a rotary knob 50 into which the D-cur portion 22 of the shaft 21 is inserted to rotate the second rotary member 42. When the shaft 21 is rotated after being inserted into the rotary knob 50, the shaft 21 and the second rotary member 42 are rotated in the same direction. The first rotary member 41 is rotated in relation to a rotational movement of the photoconductive medium 10 when the image forming device operates.
An operation of the conventional roller spacing apparatus 1 as constructed above will now be described.
The rotary knob 50 is rotated in one direction, i.e., in a counter clockwise direction, after being combined with the shaft 21 of the developing roller 20 of an image forming device or a process cartridge, which has passed a printing test of an image quality test.
As the rotary knob 50 is rotated, the second rotary member 42 and the shaft 21 are rotated together with the rotary knob 50 in the counter clockwise direction. At this time, a third rotary projection 45 and a fourth rotary projection 46 of the second rotary member 42 are rotated along a second inclination surface 36 of the spacing member 30, thereby moving the spacing member 30 to the second position of the shaft 21.
As illustrated in FIG. 3, the spacing protrusion 35 of the spacing member 30 is brought into contact with the stepped portion 12 of the driving gear 11 of the photoconductive medium 10 due to the movement of the spacing member 30 such that the developing roller 20 is spaced apart from the photoconductive medium 10 by a distance corresponding to as much as a height of the spacing protrusion 35.
The image forming device or the process cartridge thus comes into market with the developing roller 20 being spaced apart from the photoconductive medium 10. The developing roller 20 and the photoconductive medium 10 remain spaced apart from one another until the image forming device or the process cartridge is delivered to a user.
When the image forming device or the process cartridge performs a printing operation, the first rotary member 41 is rotated in the counter clockwise direction by a driving force transmitted from a main driving device of the image forming device to the first rotary member 41 through the driving gear 11 of the photoconductive medium 10. At this time, a first rotary projection 43 (lockable into a first locking portion 31) and a second rotary projection 44 (lockable into a second locking portion 32) of the first rotary member 41 are rotated along a first inclination surface 37 of the spacing member 30, thereby moving the spacing member 30 from the second position of the shaft 21 to the first position.
The spacing protrusion 35 is removed from the stepped portion 12 of the driving gear 11 of the photoconductive medium 10 by the movement of the spacing member 30, and as a result, the developing roller 20 is brought into contact with the photoconductive medium 10.
During this process, the second rotary member 42 and the developing roller 20 are not rotated because the third and the fourth rotary projections 45 and 46 of the second rotary member 42 are not locked into a third locking portion 33 and a fourth locking portion 34 until the spacing member is rotated by 180°.
After that, when the first rotary member 41 is rotated at least one time, the spacing member 30 is rotated by more than 180°. Accordingly, the third and the fourth rotary projections 45 and 46 of the second rotary member 42 are respectively-locked into the third and the fourth locking projections 33 and 34 of the spacing member 30. As a result, the rotational force of the first rotary member 41 is transmitted to the second rotary member 42, and the developing roller 20 is rotated along with the second rotary member 42 in the counter clockwise direction. That is, the photoconductive medium 10 and the developing roller 20 are rotated in close contact with each other and perform a predetermined developing operation.
When the main driving device of the image forming device stops its driving operation, the first and the second rotary projections 43 and 44 of the first rotary member 41, the third and the fourth rotary projections 45 and 46 of the second rotary member 42, and the spacing protrusion 35 of the spacing member, interacting with the aforementioned elements, maintain a contact state as illustrated in FIG. 2 as long as the user does not forcibly-rotate the shaft 21 of the developing roller by using the rotary knob 50.
However, the conventional roller spacing apparatus 1 has the spacing member 30 and the first and the second rotary members 41 and 42 located at one end portion of the shaft 21 of the developing roller 20 to space out the developing roller 20 from the photoconductive medium 10.
Accordingly, in operation, only one end portion of the developing roller 20 is spaced away from the photoconductive medium 10 by a distance corresponding to as much as the height of the spacing protrusion 35, and the opposite end portion of the developing roller 20 is not spaced apart from the photoconductive medium 10 by a distance corresponding to as much as the height of the spacing protrusion 35, and remains in the contact state with the photoconductive medium 10. As a result, an elastic layer formed on the opposite end of the developing roller 20 or on a corresponding portion of the photoconductive medium 10 must be physically and permanently compression set. Otherwise, high viscosity low molecular organic matter comes out of the elastic layer of the developing roller or the photoconductive medium, is combined with a developer, and thus is fixed to the surface of the developing roller and/or the photoconductive medium.
Since the conventional roller spacing apparatus 1 comprises complicated components, such as the spacing member 30, the first and the second rotary members 41 and 42, and the rotary knob 50, it is difficult to fabricate a metallic mold for the apparatus.
Also, in order to space out the developing roller 20 from the photoconductive medium 10, the conventional roller spacing apparatus 1 has to rotate the developing roller 20 about 180° in a direction opposite to the driving direction. Accordingly, when the developing roller 20 is rotated in the direction opposite to the direction of the driving direction, the developer is likely to flow out from the process cartridge and thus contaminate surrounding components.
Furthermore, since the conventional roller spacing apparatus 1 has no element to guide or restrict the movement of the spacing protrusion 35, which spaces out the developing roller 20 from the photoconductive medium 10, it is difficult to set the spacing protrusion 35 of the spacing member 30 above the driving gear 11 of the photoconductive medium 10. Also, when the image forming device or the process cartridge is delivered, the spacing protrusion 35 changes in position and thus a motion stability of the spacing member 30 (i.e., the ability of the spacing member 30 to remain in a predetermined position when the roller spacing apparatus 1 is moved) cannot be obtained.